Importance

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Abstract

Hitherto, in the tension control for a reel, it has been impossible to exceed the tension controlling range of about 1:10 which is determined by the tension controlling range of a single DC motor, so that for the reel which requires a tension controlling range over 1:10, a plurality of DC motors have been combined and used or the gear ratio between the reel and the DC motor has been changed to date. In this invention, attention is paid to the fact that undesirable phenomena such as a change in characteristic due to an armature reaction, and deterioration of rectification which are caused by setting the field system to a low level can be sufficiently suppressed by limiting the setting and controlling range to the low region of an armature current. The field system is set to a low level so that the ratio of the field magnetic flux to the diameter of the coil becomes a value lower than the maximum value and also so that the upper limit of the operating armature current which is practically applied is set low, thereby making it possible to perform stable tension control within a low tension range which has not been possible heretofore by a single DC motor.

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First Claim